Stress response of dogs (Canis familiaris) working with their owners in animal-assisted activities (AAA) were investigated by measuring urinary catecholamine concentrations. Two factors that possibly affect arousal for dogs were considered in this study: repeated days of participation in AAA at a special nursing home for elderly people (field investigation 1), and seat arrangements of elderly people (sitting in a circle or in parallel) for face-to-face activity (field investigation 2). In the field investigation 1, mean elevation of noradrenaline concentration (MENAC) of eight initially inexperienced dogs from pre-AAA to post-AAA linearly decreased as days passed (the slope of the regression line for MENAC plotted against nine days of repeated participation was -1.213, R^2=0.50, P<0.05). Higher elevation of adrenaline (long 15.03±9.72ng/mL vs. short 4.53±2.94ng/mL) and noradrenaline (long 12.26±8.80ng/mL vs. short 3.62±3.62ng/mL) concentrations were found when dogs were restricted their movement for a relatively long time during AAA (both P<0.05). In the field investigation 2, mean elevation of catecholamine concentrations was not significantly different between circle (12 dogs, adrenaline 10.73±9.77ng/mL; noradrenaline 7.13±8.01ng/mL) and parallel (11 dogs, adrenaline 13.37±10.63ng/mL; noradrenaline 5.70±5.19ng/mL) sitting. These results suggest that dogs can easily, even monthly participation, acclimate to an atmosphere of AAA and/or novel surroundings of a special nursing home unless they are restricted for many minutes, and that pet dogs are unlikely to suffer discomfort even if they are enclosed by unfamiliar elderly people as and when they work with their owners.